Integrated circuit devices such as transistors are formed on semiconductor wafers. The integrated circuit devices are interconnected as functional circuits through the metal lines and vias (commonly referred to as metal layers). There may be up to nine metal layers in a semiconductor wafer. The formation of the metal lines and vias are referred to as a back-end-of-process. The formation of the metal layers typically involves damascene processes, wherein copper is used to form the metal layers.
The yield in the manufacture of the metal layers significantly affects the overall yield in the manufacturing of the integrated circuits. Therefore, the problems that have the most effect on the yield need to be handled as a priority. It has been found that the generation of copper pits is the number-one problem in the back-end-of-process. Statistic results have shown that the yield loss caused by copper pits may reach as high as about 20 percent among all yield loss in the back-end-of-process.